The Centre for Environment, Fisheries and Aquaculture Science (Cefas) is an Executive Agency of the Department of Environment, Food and Rural Affairs (Defra), formerly the Ministry of Agriculture, Fisheries and Food (MAFF). It was also known previously as the Directorate of Fisheries Research (DFR). This data policy refers to data collected by the organisation under all titles.

These data have no specific confidentiality restrictions for academic users. However data are restricted for commercial requests and clearance must be obtained by BODC from Cefas before they are released.

Users must acknowledge data sources as it is not ethical to publish data without proper attribution. Any publication or other output resulting from usage of the data should include an acknowledgement.

The recommended acknowledgement is: "This study uses data from the Centre for Environment, Fisheries and Aquaculture Science (Cefas), provided by the British Oceanographic Data Centre."

Guildline 8705 CTD

The 8705 CTD is a conductivity-temperature-pressure profiler designed for marine applications down to depths of 6000 m. The instrument includes an anodised aluminium tube with a steel cage to protect the temperature and conductivity sensors and a urethane cap to protect the pressure sensor.

Specifications

Parameter

Range

Accuracy

Resolution

Stability

Response time

Pressure

0 to 6000 dbar

± 0.15% of full range

± 0.01% of full range

-

< 50 ms

Temperature

-2 to 30 °C

± 0.005 °C

± 0.0005 °C

± 0.002 °C over 30 days

± 0.0025°C over 6 months

< 50 ms

Conductivity *

100 ppm to 40 ppt

± 0.005 ppt

± 0.001 ppt

± 0.002 ppt over 6 months

< 50 ms

* Conductivity specifications are given in terms of equivalent salinity

RV Cirolana Cruise 8/92 CTD Data Documentation

Instrumentation

The CTD used was 8705.

Sampling Protocol

Sixty-five CTD profiles were obtained during the cruise. Reversing thermometers were fitted to the Niskin used to collect samples. Samples for salinity analysis were collected from both the near surface and close to the sea bed.

Calibration

Not all the calibration data collected were used to calibrate the CTD sensors for the following reasons:

Thermometer differences too large (>0.04).

It was clear from the profiles obtained at time of station that some T and/or S values measured by the CTD were variable, believed real, not an instrument malfunction, and unsuitable for calibration use. 21 data sampling points were not used because of this.

The salinity analysis of water samples from station 167 (top) onwards was suspect, possibly due to room temperature changes. These 28 samples were not used for the calibration.

Pressure

The pressure sensor was corrected using the laboratory calibration of August 1992 at T = 16.2 °C.

P(cor) = P(ctd) - 1.4

Temperature

The temperature sensor was corrected using laboratory calibration of August 1992.

T(cor) = T(ctd) + dT dT = a*T(ctd)*T(ctd) + b*T(ctd) + c

where:

a = -1.18042e-05 b = 3.74e-04 c = 1.0502e-02

This amounts to 13 mK for temperatures encountered during the cruise, of about 18 °C.

A comparison between thermometer and uncorrected CTD temperatures is shown in Fig. 1. If it is assumed that the thermometer temperatures are accurate to 0.02°C and the CTD to 0.01 °C then all differences to within 0.03 °C of the Laboratory calibration are acceptable i.e. those within 43 mK and - 17 mK. Nine out of ninety-five values were found to be outside this range.

The mean of the eighty-six differences was found to be 15 mK which is in excellent agreement with the laboratory calibration.

Salinity

Fig. 2 shows how the uncorrected CTD salinity estimates compared with salinity measurements from the salinometer. (Note that CTD measurements of pressure, temperature and conductivity have not been corrected; the CTD salinity is derived from uncorrected observations). This plot suggests a different CTD response before and after station 101, also seen in Fig. 3, which shows how the conductivity ratio of the CTD and water samples varies during the cruise.

Fig. 2 and Fig. 3 suggest a change in response of the CTD near station 102. Consequently, the salinity samples were divided into two parts for the calibration.

CR(cor) = CR(ctd)*[ a*T(cor) + b*P(cor) + c ]

where:

Stations 10 to 101 inclusive

a = -0.267503539e-04 b = -0.200824708e-05 c = 0.100047932e+01

The rms difference between salinometer and corrected CTD salinity was 0.005 for 50 observations.

Stations 102 to 167

a = 0.761912360e-04 b = -0.215006427e-05 c = 0.998961505e+00

The rms difference between salinometer and corrected CTD salinity was 0.005 for 44 observations.

Fig. 4 shows how effective the sensor coefficients are in correcting the CTD salinity estimates for the calibration samples. The offset and discontinuity seen in Fig. 2 and Fig. 3 have been removed.

Fig. 5 shows the difference between water sample (salinometer) and CTD salinity before and after the calibration of the conductivity sensor has been applied. Note that for the upper histogram the CTD salinity has been derived from corrected CTD pressure and temperature but uncorrected conductivity ratio. This figure therefore indicates how effective the conductivity calibration has been. If it is assumed that the CTD salinity is accurate to 0.01 and the salinometer is accurate to 0.006, then differences less than or equal to 0.016 are acceptable. Only one of ninety- four data values is outside this range after the sensor calibrations have been applied.

CTD stations 167 to 213 were corrected using the coefficients for stations 102 to 167.

Suspended Load

The %transmission sensor readings were converted to suspended loads using the following calibration:

SUSP.LOAD = -8.61 * LOGe(%TRANSMISSION) + 33.58

General Data Screening carried out by BODC

BODC screen both the series header qualifying information and the parameter values in the data cycles themselves.

Header information is inspected for:

Irregularities such as unfeasible values

Inconsistencies between related information, for example:

Times for instrument deployment and for start/end of data series

Length of record and the number of data cycles/cycle interval

Parameters expected and the parameters actually present in the data cycles

Originator's comments on meter/mooring performance and data quality

Documents are written by BODC highlighting irregularities which cannot be resolved.

Data cycles are inspected using time or depth series plots of all parameters. Currents are additionally inspected using vector scatter plots and time series plots of North and East velocity components. These presentations undergo intrinsic and extrinsic screening to detect infeasible values within the data cycles themselves and inconsistencies as seen when comparing characteristics of adjacent data sets displaced with respect to depth, position or time. Values suspected of being of non-oceanographic origin may be tagged with the BODC flag denoting suspect value; the data values will not be altered.

The following types of irregularity, each relying on visual detection in the plot, are amongst those which may be flagged as suspect:

If a large percentage of the data is affected by irregularities then a Problem Report will be written rather than flagging the individual suspect values. Problem Reports are also used to highlight irregularities seen in the graphical data presentations.

Inconsistencies between the characteristics of the data set and those of its neighbours are sought and, where necessary, documented. This covers inconsistencies such as the following:

Maximum and minimum values of parameters (spikes excluded).

The occurrence of meteorological events.

This intrinsic and extrinsic screening of the parameter values seeks to confirm the qualifying information and the source laboratory's comments on the series. In screening and collating information, every care is taken to ensure that errors of BODC making are not introduced.

Joint Nutrient Study I (JoNuS)

Concerns by the scientific community about the impact of nutrient inputs to the sea; a lack of information on inputs from the UK and on the spatial and temporal distribution and cycling of nutrients in UK waters provided the impetus for the JoNuS project.

The project sought to quantify the input of nitrogen, phosphorus and silicon from UK estuaries to the North Sea through a good understanding of the estuarine processes that control the flow of these nutrients. It focussed on the Great Ouse/Wash and the Humber outflows. Its specific objectives were:

To measure the fluxes of nutrient elements (N, P, Si) through selected major estuaries on a quantitative annual basis in order to determine the net input to the sea resulting from gross river inputs.

To quantify the processes controlling the fluxes of nutrients through estuaries.

The Centre for Environment, Fisheries and Aquaculture Science (CEFAS) hosted the project, which involved scientists from CEFAS, the University of East Anglia, the University of Essex, the Plymouth Marine Laboratory and the National Rivers Authority (now the Environment Agency). It was funded by the then Ministry of Agriculture, Fisheries and Food (MAFF) and the Department of Environment, now the Department of Environment, Food and Rural Affairs (Defra).

The project ran from April 1990 to March 1995, with marine field data collection between May 1990 and December 1993. Data collection involved ship based surveys which were complemented by estuarine transects and specific process studies.

Initially, the surveys were on a quarterly basis up to October 1992, however monthly surveys were carried out during 1993. During this intensive survey period, the programme focused on the Great Ouse/Wash; with a continuing, but lower level, of activity devoted to the Humber. An additional multi-project cruise, carried out in January 1995, also complemented the JoNuS data set. Further details of the JoNuS I cruises are provided below: